Low friction pawl



y 3 1960 H. M. PASSMAN 2,938,606

LOW FRICTION PAWL Filed NOV. 21, 1956 FIG 2 INVEN TOR. HARRP M. PA ssmAn A "r TORNE vs United tates Patent LOW FRICTION PAWL Harry M. Passman, Cedar Rapids, Iowa, assignor to {lollins Radio (Iompany, (Iedar Rapids, Iowa, at corporation of Iowa Filed Nov. 21, 1956, Ser. No. 623,631

1 Claim. ((11. 188-69) This invention relates to positioning systems and more particularly to pawls for use therein.

Prior to this invention automatic positioning systems have involved a motor driving a seeking switch through a torque limiting clutch with a stop wheel and pawl positioning the seeking switch. Under certain applications the pawl would resist being pulled out of its notch in the stop wheel. Attempts to alleviate the problem by shaping the notch in the stop Wheel fail because the pawl then skips when it should enter into the notch to stop the system. A pawl that stops the system usually also resists being pulled out under conditions where the motor must be running.

Accordingly, it is an object of the invention to provide a pawl which will be readily pulled out of engagement with its cooperating stop wheel.

It is an object of this invention to provide a pawl cooperative with stop wheels which provides certainty in positioning yet is capable of facile repositioning.

It is a feature of the invention that a small, hardened steel ball is inserted in the face of the pawl engaging the stop wheel.

Further objects, features, and advantages of the invention will become apparent from the following description and claims when read in conjunction with the drawing in which:

Figure 1 shows a portion of an automatic positioning system employing a pawl made according to the invention, and

Figure 2 shows a stop wheel and a pawl made according to the invention used in the system of Figure 1.

In Figure 1 a stop wheel 10, mounted on a shaft 9, is driven by a motor 11. Also, a seeking switch 12 is driven simultaneously with stop wheel 16 Coupling motor 11 to shaft 9 is a torque limiting clutch 13 which permits the motor to coast after it has been turned off in the cycle of operation. Motor 11 is energized from a power supply connected to terminal 14 through a set of switch contacts 15. The seeking switch 12 shown is a four position type wherein the open circuit made by rotor 16 opens a control circuit established by a similar remote switch, not shown. When the remote switch establishes a new circuit, one of the fixed contacts, such as 1'7, is grounded, grounding wiper 18 through rotor 16.

Upon grounding wiper 18, a circuit to the power source terminal 14 through solenoid 19 is completed. Upon this energization, solenoid 19 pulls pawl 20 out of notch 21 of stop wheel 10. At the same time, switch 15 is closed, energizing motor 11. The shaft 9 is rotated by motor 11 until the grounded circuit is opened by the notch in rotor 16. At this time the solenoid is de-cn- 2,938,606 Patented May 31, 1960 2 ergized, the pawl is pulled into a notch by spring 22 to arrest the motion of stop wheel 111, and the motor circuit is broken at 15. A complete description of the prior system is best seen in the United States Patent No. 2,476,673 to May et al., issued July 19, 1949.

On occasions where motor 11 is still moving or some other type of load forces stop wheel 10 into pawl 20, it is obvious that a binding occurs which prevents the pawl from pulling out of a notch by solely the force of solenoid 19.

in accord with the invention, the pawl 20 is constructed as shown in Figure 2. Here, stop wheel 10, mounted on axle 9, is coplanar with pawl 2d. Pawl 20 is pivotally mounted on a fixed axle 23 which may be a pivot in the armature arrangement of solenoid 19. On the tip 24 which engages notch 21 of the stop wheel, a ball is provided. This ball is on the face 25 which bears the undesired friction load. The ball 26 is mounted by being inserted into a pocket in the pawl and being swaged in lightly as evidenced by the mark 27. The ball is preferably of hardenable bearing material such as a carbon steel or a beryllium alloy. The stop wheel is of similar material while the pawl is usually made of beryllium copper hardened to the proper degree.

In operation, the pawl is pulled into slot 21 by spring 22. The engaging face 25 of pawl 24) intersects with the side of the notch 21 to stop wheel 10. For repositioning, the solenoid 19 pulls pawl 20 out of the slot with the ball 25 rolling in its pocket, reducing the pawl pull-out friction. The motor, either running or started by the pull-out turns the stop wheel and seeking switch until the new position is found. The relay is de-energized, the pawl drops into a slot, and the system stops.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited because changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claim.

I claim:

In a shaft positioning system of the type which includes a stop wheel having a notched periphery, and a pivotally mounted pawl having a notch engaging portion thereon; a friction reducing means for said notch engaging portion of said pawl comprising, a socket formed in the stopping edge of said notch engaging portion of said pawl, a ball means freely received in said socket, and means rotatably retaining said ball in said socket, said notch engaging portion of said pawl including said ball means having sufiicient width to fit snugly within the notched periphery of said stop wheel whereby the friction between the stopping edge of said pawl and the peripheral notch of said stop wheel will be substantially reduced.

References Cited in the file of this patent UNITED STATES PATENTS 619,985 Niles Feb. 21, 1899 1,834,448 Ellis Dec. 1, 1931 1,973,891 Bankert Sept. 18, 1934 2,141,266 Dickerson Dec. 27, 1938 2,485,105 McKnight Oct. 18, 1949 2,592,064 Peterson et a1. Apr. 8, 1952 FOREIGN PATENTS 814,144 France Mar. 8, 1937 

